Polymerization

A. General considerations

1. Cellular building blocks

a) Polysaccharides

b) Proteins

c) Lipids and membranes

d) Nucleic Acids

2. Dehydration Synthesis Problem

B. Carbohydrate biosynthesis

1. Glucose 6-phosphate is the starting point: Products

a) Free Glucose

b) Cell Wall Polysaccharides (cellulose, hemicelluloses in plants; murein in bacteria)

c) Glycogen and starch

d) Other monosaccharides: fructose & galactose

e) Disaccharides (12C sugars): lactose & sucrose

2. Cell Wall Polysaccharides

a) Cellulose

(1) A 1-4glucan polymer

(2) NDP-glucose + (glucose)n NDP + (glucose)n+1

b) Murein in bacterial cell walls

(1) 1-4 disaccharide attached to a tetrapeptide

(2) cross-linked to form a rigid shell

(3) produced outside the cell membrane

3. Glycogen and starch as storage products

a) Nucleoside diphosphate attaches to glucose and adds the glucosyl residue to the growing polysaccharide chain

b) Reaction is a dehydration synthesis reaction as the C1 H is attached to the C4 OH group

4. Pyruvate to Glucose 6-phosphate pathway is universal in cells, it is called gluconucleogenesis

C. Protein synthesis

1. Protenoids

a) Mixtures of aa's are heated to 170°C qiuckly or warmed with polyphosphates at 50 to 60° C for a few days

b) Can be used as primitive enzymes, i.e. some protenoid mixtures enhance reactions formimg ester bonds

2. Peptide bonds - amine group (NHH) links to an adjacent acid group (COOH) and a molecule of water (H2O) is released.

D. Lipids and Membranes

1. Fatty acid synthesis in the cell

a) Malonic acid is the precursor molecule

b) Complete synthesis take place in the cytoplasm

c) Production of Palmitic acid

2. Component precursors

a) Glycerol

b) Fatty acids

c) Phosphate

3. Synthesis

a) Dry and incubate at 65°C for 1 week

b) Upon later wetting and sonication, micelles and vesicles may form

c) Non-clay silicates may promote these reactions

E. Nucleic Acids

1. Polyphosphoric esters + adenine + pentose adenoside (nucleoside) formation

2. Nucleosides + polyphosphate nucleotides formed

a) Reactions require heat or uv

b) Phosphate links at 2 to 5 carbon position

c) Nucleotides in DNA link 3-5; prebiotic versions appear to favor 2-5 linkage

3. CG and AU pairs occur spontaneous without the backbone

F. Dehydration Synthesis Problem

1. Generic dehydration synthesis reactions are not favored in water

a) A + A A2 + H2O

b) LeChatelier's Principle

2. Projected sites

a) Ephemeral ponds >> freshwater sites

(1) Rainwater flux is actually pretty extensive

b) Soils subjected to aperiodic wet/dry cycles

c) Tidal zones

(1) PreCambrian tides were more extensive than today ( the moon was closer)

(2) Subaerial exposure to UV

d) Aerosol Theory of Carl Wose

(1) Monomers dissolve in water droplets

(2) Droplets lose water as they drop through the atmospherere

(3) H2O loss drives reactions toward polymerization

3. Condensing agents

a) Some molecules can polymerize by incorporating the water into a reaction product, vis. dicyclohexyl carbodiimide binds aa's by incorporating the water into a derivative of urea

b) E.g.

(1) Cyanate

(2) Cyanogen

(3) Cyanamide dicyandiamide (which acts as agent)

(4) Easily derived from HCN

c) These compounds can also form phosphate and acetate esters from alcohols

G. Polyphosphates

1. Can be formed prebiotically by heat

2. Also derived from above condensing agents

3. Polyphosphates + aa's [uv or gentle heating] polypetides

4. Stable in oceans/aqueous solutions

5. Promote numerous biologically important reactions


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update 4 October 2005